Interference: Cutting the Line Between Defender and Defended

Long-range pieces, queens, rooks and bishops, often defend from a distance along a file, rank, or diagonal. That defence only works while the line between them stays open. Interference drops a piece onto that line. Suddenly the defender is cut off, and whatever it was guarding becomes loose.

The interfering piece is often offered as a sacrifice. That does not matter if capturing it costs the opponent even more, or if it cannot be captured at all because it is protected.

Interference is related to deflection and to removing the defender, but the method differs. Deflection lures the defender away; removing the defender captures it; interference leaves the defender exactly where it is and blocks its line. When the defender cannot be attacked or chased, blocking it is often the only option.

It is also the mirror image of clearance. Clearance opens your own lines; interference closes the opponent's.

A special case appears when two enemy long-range pieces guard each other's lines through the same square. A piece dropped on the crossing point can block both at once: whichever piece captures it closes the other's line. These double interferences are rarer in practical games, but the simple version, one defender and one blocking piece, comes up constantly.

Trace every long-range defence in the enemy camp. For each piece that is protected only once, follow the line to its defender and list the squares in between. Can any of your pieces reach one of those squares, ideally with a threat? An interfering move that also attacks something forces the opponent to deal with two problems in one move.

Pay special attention to pieces defended by a queen far away. Queens defend a lot, from a distance, and are easy to cut off. The cut-off defenders you overlook in your own games are good material to drill.